Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities (Continuous Unrealized Loss Position) (Details)

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Marketable Securities (Continuous Unrealized Loss Position) (Details) (USD $)
 3 Months Ended 9 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2012
Mar. 31, 2011
Investments in an Unrealized Loss Position        
Fair Value $ 478,842,000   $ 478,842,000  
Gross Unrealized Losses, less than 12 months (875,000) [1]   (875,000) [1]  
Gross Unrealized Losses, 12 Months or Longer 0   0  
Net realized securities gains 100,000 400,000 700,000 1,900,000
Months in Loss Position Not Exceeding this Period 12      
U.S. Treasury securities
        
Investments in an Unrealized Loss Position        
Fair Value 39,027,000   39,027,000  
Gross Unrealized Losses, less than 12 months (45,000) [1]   (45,000) [1]  
Gross Unrealized Losses, 12 Months or Longer 0   0  
U.S. Government agency securities
        
Investments in an Unrealized Loss Position        
Fair Value 196,537,000   196,537,000  
Gross Unrealized Losses, less than 12 months (310,000) [1]   (310,000) [1]  
Gross Unrealized Losses, 12 Months or Longer 0   0  
Municipal securities
        
Investments in an Unrealized Loss Position        
Fair Value 6,747,000   6,747,000  
Gross Unrealized Losses, less than 12 months (5,000) [1]   (5,000) [1]  
Gross Unrealized Losses, 12 Months or Longer 0   0  
Corporate debt securities
        
Investments in an Unrealized Loss Position        
Fair Value 230,504,000   230,504,000  
Gross Unrealized Losses, less than 12 months (513,000) [1]   (513,000) [1]  
Gross Unrealized Losses, 12 Months or Longer 0   0  
Sovereign securities
        
Investments in an Unrealized Loss Position        
Fair Value 6,027,000   6,027,000  
Gross Unrealized Losses, less than 12 months (2,000) [1]   (2,000) [1]  
Gross Unrealized Losses, 12 Months or Longer $ 0   $ 0  
Corporate and Government Securities [Member]
        
Investments in an Unrealized Loss Position        
Securities, Contractual Maturity Date (in years), High     3  
[1] Of the total gross unrealized losses, there were no amounts that, as of March 31, 2012, had been in a continuous loss position for 12 months or more.